Technical Field
The invention relates to a sealless canned motor pump, more particularly to, an anti-corrosion and sealless canned motor pump including a bearing monitor device. The sealless canned motor pump comprises a canned motor and a pump integrated into one unit. An inner rotor and a stator windings of the motor are protected by an anti-corrosion material and are in direct contact with transferred fluid, such as chemical liquid in the PCB manufacturing device, is toxic, flammable and corrosive. The motor, including an induction motor (induction canned motor pump) or a permanent magnet pump (permanent magnet canned motor pump), are popular among industrial use requiring leakage-free. Moreover, the inner rotor of the sealless canned motor pump, in directly contact with the transferred fluid, comprise a slide bearing made of ceramic material, such as graphite, aluminum oxides or silicon carbides. However, the wear of the bearing may cause the inner rotor to rotate eccentrically so that a stationary shaft must bear greater centrifugal force and moment thereof, making the inner rotor and a containment shell collide with each other to be damaged and the fluid may be leaked. Therefore, the structure of the motor shaft system becomes one the focus of the design. A method for preventing leakage with high reliability is to dispose a bearing monitor device in the pump.
Therefore, the invention discloses a permanent magnet canned motor pump made of plastic or including a plastic liner in order to improve the structure stiffness of the stationary shaft and a monitor devise can be installed in the pump.
Related Art
A metal induction canned motor pump comprises a cylindrical can made of a metal thin plate with low magnetic permeability and anti-corrosion for encapsulating a inner rotor and a stator. The can is assembled inside the stator for isolating fluid and windings. Another metal plate is used for encapsulating a squirrel cage inner rotor to isolate the fluid as well. Therefore, air gap of the motor is a single-sided radial distance between a silicon-steel teeth part of the stator and a silicon-steel teeth part of the inner rotor. Most of the widths of the air gap are less than 3 millimeters (mm) so the motor characteristic of the above-mentioned motor is a motor structure with small air gap. The sealless canned motor pump which is adopted for transferring a clean and non-corrosive fluid, such as an automobile water cooling pump, are made with a heat-resisting plastic material with temperature resistance and limited anti-corrosion ability, such as polyphenylene sulfide (PPS) and the heat-resisting plastic material is used for encapsulating the stator and the inner rotor. The singled-sided encapsulation thickness of the heat-resisting plastic material is above 1.5 mm, and the width of the total air gap is above 4 mm. That is, the characteristic of the motor is a structure with bigger air gap. In order to transmit chemical fluid with high toxic and high corrosion, such as hydrofluoric acid, an anti-corrosion plastic component or liner, such as polypropene (PP), or fluoropolymer, are adopted for encapsulating the stator and the inner rotor. Because of the adoption of the anti-corrosion plastic material, the structure strength of the motor shaft system becomes one of the focuses of the design. The types of the motor system are divided into a rotary shaft and a stationary shaft. The invention provides a preferable stationary shaft system whose single-sided encapsulation thickness with allowance is above 3 mm and most of the width of the total air gap is above 7 mm so that the characteristic of the motor according to the invention is the motor structure with bigger air gap. Therefore, a permanent magnet synchronous motor is a preferable choice for the pump with bigger air gap. Although the sealless canned motor pump comprises a slide bearing made of ceramic material, the bearing may be worn because of the bearing wear, dry-running or excessive vibration. Therefore, disposing a monitor device monitoring the wear of the bearing is necessary to improve its reliability. Moreover, the monitor device may be a hall sensor so the driving method of the permanent magnet canned motor pump can drive with both sensor or sensorless method. Thus, the dependency of certain driver is reduced and user may have a wider choice of equipment.
The following cases are solutions to the problem of the sealless canned motor pump including stationary shaft structure, sensorless driving, sensor driving and bearing wear detection. The contents of the cases are described hereinafter:
Case 1:
Taiwan patent number: M369391 permanent magnet canned motor pump, 2009. The invention discloses a pump which is used in high-temperature and corrosive condition. A motor structure comprises a cantilever stationary structure and an inner motor with a radial air gap. The encapsulation thickness with corrosion allowance is 3 mm and the total air gap is 8 mm. A sensorless method disclosed in the invention is that calculating a magnetic pole position to drive the permanent magnet pump, and the stiff composited stationary structure satisfies the requirement for high temperature and high power usage. However, the structure of the invention does not have any bearing wear detecting ability.
Case 2:
Japan patent number JP2005344589A: CANNED MOTOR PUMP, which is a permanent magnet canned motor pump applied in engine cooling. A pump with low power in the invention is a simple stationary shaft structure. A ceramic shaft is supported by heat-resisting plastic components including a triangle front support and a pump containment shell. Second magnets and hall sensors are installed in the inner space of an inner rotor yoke of main magnets for detecting a magnetic pole position to drive the permanent magnet pump. The hall sensor extends outwardly from a bottom side of a containment shell. The magnets of the inner rotor also extend axially accordingly to reduce the independent extending length of the hall sensor. Since only clean fluid is transferred by the pump, it is not necessary to concern about the wear of the bearings. The simple stationary structure is adopted but the addition of the length of the magnets may increase the manufacturing cost, and only the magnetic flux which is scattered on a surface of the magnets are detected, it is unfavorable for detecting accurate magnetic pole position.
Case 3:
Japan patent number JP2008220008A: BRUSHLESS MOTOR AND FLUID PUMP DEVICE, 2008, which discloses a permanent magnet canned motor pump applied in engine cooling. A pump in the invention with low power is a simple stationary shaft structure. A ceramic shaft is supported by heat-resisting plastic components including a triangle front support and a pump containment shell. A hall sensor and a driving circuit board thereof are installed on the outside of the containment shell to drive the permanent magnet pump. Magnet extends axially to make a rear end of the magnet close to the hall sensor. Furthermore, the shape of the rear end of the magnet is processed into a slope shape, so that the magnetic flux of the magnet may pass in an oblique direction and through the hall sensor on the board for enhancing the accuracy of the detection of the magnetic pole position. Since only clean fluid is transferred by the pump, it is not necessary to concern about the wear of the bearings. The simple stationary structure is adopted but the addition of the length of the magnets may increase the manufacturing cost, and only the magnetic flux which is scattered on a surface of the magnets are detected, it is unfavorable for detecting accurate magnetic pole position.
Case 4:
U.S. Pat. No. 4,211,973A: Apparatus for detecting faults to be occurred or initially happening in a running electric rotary machine, 1980, which is applied in an induction canned motor pump. Signal coil pairs are long enough to cover the total length of a stator yoke. The signal coil pairs may output a periodic voltage signals including a synchronous induction voltage with main magnetic flux, and a inner rotor electromotive harmonic voltage due to a inner rotor slip. When a bearing is worn, the size of an air gap is slightly changed, and the voltage signals which is output by the signal coil pairs is varied accordingly. When the two signal coil pairs are at the opposite radial position of the teeth part of the stator respectively, the output voltage is neutralized by opposite main magnetic flux and leaves the periodic harmonic voltage. When the bearing is worn to cause the inner rotor to rotate eccentrically, the periodic harmonic voltage is increased, which is applied in an axial air gap induction motor and a radial air gap induction motor. Such method may be utilized to detect the problem of motor power or the motor winding, such as the unbalance problem of the three phase windings. But the invention is only used for detecting the wear of the radial bearing of the induction motor, not for detecting the wear of an axial thrust bearing.
Case 5:
U.S. Pat. No. 5,926,001A: Canned motor bearing wear monitor device, 1999, which is applied in an induction canned-motor pump. Four holes are formed in the inner side of four perpendicular teeth parts at each of two opposite end of a stator, respectively so that four of eight coils are installed in the respective holes at the one end and the other are installed at the opposite end. Each of the two corresponding holes at opposite end has the same special angle so that the eight coils may detect the radial wear, axial wear, oblique wear of a bearing.
Case 6:
U.S. Pat. No. 5,955,880A: Sealless pump inner rotor position and bearing monitor, 1999, which is applied in an induction canned-motor pump. Two coils and yokes with different magnetic poles form a high-frequency excitation coil set. The two coils are fixed on an outer surface of a can by the yokes in parallel to each other and at the axial position on an outer side of each end of a stator, respectively. The magnetic flux of the coil set passes through the can to and enters the outer space of the two ends of an inner rotor. Then the flux reversely returns back to the different magnetic pole coil via a magnetic conductive material on a plate at two side ends of the inner rotor of the shaft. Therefore, a closed-end magnetic circuit is formed, that is, the magnetic conductive material and the coil set are concentric to each other. The coil comprises three wires winding together and the one of the wires is used for exciting in high frequency to the other two wires to become the two signal wire. One of the signal wires is used for radial detection and the other is used for axial detection. When an axial wear happens on one side of a bearing, the radial position of the plate is moved in a radial direction, which causes the plate close to or away from the coil set. Therefore, the magnetic reluctance of the magnetic circuit is changed and the output voltage of the magnetic circuit is varied as well.
When four coil set perpendicular to each other are installed on the radial position, the radial wear of the bearing may be detected. When the coil sets and the plates are both installed on the two side of the inner rotor, the axial movement may be detected further. The signal processing of the axial detection is comparing two voltage signals from the coil sets at two sides of the inner rotor with each other for calculating the axial movement of the inner rotor. In addition, the high-frequency signal between 1K to 4K may prevent the harmonic signal interference of the coil. Moreover, in order to reduce the harmonic signal interference, a magnetic flux blocking device is further installed on a rear end of the stator coil.
Case 7:
U.S. Pat. No. 6,114,966A: Motor having a bearing wear monitor device, 2000, which is applied in an induction canned motor pump. The invention indeed indicates that disposing several signal coil pairs at two opposite ends of a stator may detect the radial wear of a bearing. However, when repairing a motor, including replacing a stator, a inner rotor, a spindle or signal coil pairs, a user may not make the mechanical axial positioning of the stator and the inner rotor to meet with their electrical axial positioning, or the user may not wind the coil to be positioned at the previous position, thereby generating an unusual signal. That is to say, the monitor device may adjust the relative positions and zeroing the signal of axial wear. The method is that because the thickness of the inner rotor is greater than that of the stator, when the motor is assembled, the distance between a inner rotor side of a shaft and a stator side of the shaft. The inner rotor side faces the center of the coil, the protrusion of the inner rotor protrudes from a rear end of the stator so a rear end of the inner rotor completely covers the coil without any radial allowance. Therefore, when the thrust bearing is worn and the inner rotor is moved forward, the coil signal at the front end is changed obviously, and the coil signal at the rear end is changed slightly.
Case 8:
U.S. Pat. No. 6,429,781B2: Axial bearing wear detector device for canned motor, 2002, which is applied to an induction canned motor pump. The device comprises a coil set which has two coils at two opposite teeth part of a stator, respectively, and forming a space angle of 180 degrees. Although the invention clearly indicates that disposing several signal coil pairs at the front and rear ends of the stator may detect the axial wear of a bearing, the axial lengths of wear rings which are installed at a front end and a rear end of a motor are greater than the axial lengths of thrust bearings which are installed at a front end and a rear end of the inner rotor. The inner rotor may be moved between the wear rings about ±2.5 mm in a free radial direction. A monitor device for detecting the axial wear of the bearing must distinguish abnormal axial movement of the inner rotor from normal axial movement of the inner rotor. In other words, the actual wear of the bearing needs to be detected. The invention enables a reference circuit and a dead spot circuit to be compared with each other in order to detect a coil signal for determining whether the axial movement of the inner rotor is within a normal range.
Case 9:
U.S. Pat. No. 7,019,661B2: Axial wear detector of bearing in canned motor, 2006, which is applied to an induction canned motor. The method for detecting coils in this invention is similar to the case 8. The invention clearly indicates that disposing several signal coil pairs at the front and rear ends of a stator may detect the axial wear of a bearing and generate a signal, and a wear value may be detected accurately when the signal is zeroed. However, the value of voltage signal which is output by the signal coil pairs may be affected by the operating voltage of the motor to cause the electromigration, thereby zeroing the signal difficultly. In other words, the wear value of the bearing is not accurate. The invention provides a method for processing the signal and a device thereof may zero the signal certainly.
The solution to the induction canned motor pump and the permanent magnet canned motor pump are divided into three types, shown as follows:
1. A monitor device is installed for detecting a bearing to improve the reliability of a pump.
2. A hall sensor is installed for driving a pump conveniently, but a magnet must be lengthened.
3. The stiffness of a stationary shaft is enhanced for improving the reliability of a pump.
The above-mentioned solutions to their corresponding problems may be feasible to be practiced, but the above-mentioned cases may not enhance the stiffness of the stationary shaft and dispose a monitor device for improving the reliability at the same time. A permanent magnet canned motor pump which is disclosed in this invention must overcome the following problems:
Problem 1: The weakness of the strength of a material.
Improve the structure strength to prevent the problem that the strength of an anti-corrosion plastic structure or liner is easily reduced when the temperature is above 85° C., and the reliability of a pump is improved without disposing a monitor device.
Problem 2: The requirement for detecting the wear of the bearing.
In order to satisfy the safety requirement for transmitting a high toxic and high corrosive chemical fluid, a monitor device is installed for detecting the wear condition of the bearing continuously to improve the reliability of the pump.
Problem 3: The low cost requirement for being with the motor characteristic of bigger air gap.
A permanent magnet motor is a preferable choice for the motor with bigger air gap, but a large amount of expensive magnets is needed. Increasing the length of the main magnet is used for providing a signal source of a monitor element. Therefore, the cost of the magnets is relatively increased.
Problem 4: Prevent a harmonic interference from the driving of a high frequency Pulse width modulation (PWM) signal of the permanent magnet motor.
The structure of the monitor device must the harmonic interference from the driving of a high frequency PWM electric power.
Problem 5: A requirement for receiving a signal with better quality when the monitor device is enabled.
The inner rotor of the canned motor pump has a larger axial free-movement space in high-anti-corrosion use, so the magnetic flux of the monitor device is easily bent and the drifting of signal which is due to the different voltage supply must be avoided.
Problem 6: The components are easily repaired and replaced.
When the component is repaired or replaced, the problem of the positioning or other personal factors must be avoided.
The present invention enhances the stiffness of the stationary shaft of a permanent magnet canned motor pump within any power range, under a reasonable cost, and a monitor device can be installed according to requirement. Therefore, the reliability is ensured and the life span is extended, and furthermore, the present invention is suitable for the simple stationary shaft structure and a composited shaft structure.